The Halo Occupation Distribution of Active Galactic Nuclei

TL;DR

This study uses cosmological simulations to analyze how environmental factors influence the distribution and clustering of low luminosity AGN within dark matter halos, revealing detailed occupation statistics and luminosity-halo relationships.

Contribution

It introduces a comprehensive model of AGN halo occupation distribution incorporating environmental effects, decomposing into central and satellite contributions, and analyzing luminosity functions across redshifts.

Findings

Central AGN CLF follows a log-normal distribution with redshift-dependent mean and scatter.

Peak AGN luminosity correlates more tightly with halo mass than instantaneous luminosity.

The mean occupation function can be modeled as a softened step for centrals and a power law for satellites.

Abstract

Using a fully cosmological hydrodynamic simulation that self-consistently incorporates the growth and feedback of supermassive black holes and the physics of galaxy formation, we examine the effects of environmental factors (e.g., local gas density, black hole feedback) on the halo occupation distribution of low luminosity active galactic nuclei (AGN). We decompose the mean occupation function into central and satellite contribution and compute the conditional luminosity functions (CLF). The CLF of the central AGN follows a log-normal distribution with the mean increasing and scatter decreasing with increasing redshifts. We analyze the light curves of individual AGN and show that the peak luminosity of the AGN has a tighter correlation with halo mass compared to instantaneous luminosity. We also compute the CLF of satellite AGN at a given central AGN luminosity. We do not see any significant correlation between the number of satellites with the luminosity of the central AGN at a fixed halo mass. We also show that for a sample of AGN with luminosity above 10^42 ergs/s the mean occupation function can be modeled as a softened step function for central AGN and a power law for the satellite population. The radial distribution of AGN inside halos follows a power law at all redshifts with a mean index of -2.33 +/- 0.08. Incorporating the environmental dependence of supermassive black hole accretion and feedback, our formalism provides a theoretical tool for interpreting current and future measurements of AGN clustering.